Using main colour and the smaller needles cast on 40(44) sts and divide them onto four needles, 10(11) sts each. The beginning of round is between needles IV and I. Work twisted ribbing in the round for 8(9) cm. Knit 2 rounds. On the first round increase 1 st per needle = 44(48) sts.
Switch to the larger needles and begin the colourwork pattern on row 2 of chart I(II). Then work rows 3–15(16) of the chart.
Continue on row 16(17): work the 11(12) sts on needle I, work the first 9(10) sts of needle II (marked in red) using a different-coloured yarn (thumb hole). Move the 9(10) sts back to the left-hand needle and work to end of row following the chart.
Women’s size: Work rows 17–51. On row 42, 1 st decreased on needles II and IV. On rows 43–51, 1 st decreased on each needle.
Men’s size: Work rows 18–54. On row 44, 1 st decreased on needles I and III. On rows 45–54, 1 st decreased on each needle.
Break the yarn and pull it through the sts. Securely weave in.
Mirror left mitten and work the thumb hole on needle III.
Remove the different-coloured yarn. Using the larger needles pick up the sts from the top and bottom edges of the thumb hole. Pick up additional sts from both sides for 19(21) sts in total. Divide the sts onto three needles and work stockinette st in the round using main colour.
When you have worked for 5(5,5) cm or when the mitten covers half your thumbnail, work the top decreases: k2tog at the end of each needle until 4(3) sts remain. Then k1 and pass the other sts over from left to right. Securely weave in.
Steam the mittens lightly.